The Prevalence of Sleep Apnea in Iran: a Systematic Review and Meta-Analysis.

Background
Sleep apnea is a common sleep disorder which is associated with cardiovascular diseases, diabetes and stroke. Different studies conducted in Iran have reported different prevalence for sleep apnea. The aim of the present study was to determine the prevalence of sleep apnea in Iran.


Materials and Methods
In this study, 42 studies that have been published in Farsi and English languages were selected with no time limit up to the March of 2018. Article search was conducted using "prevalence", "frequency", "sleep apnea" and "obstructive sleep apnea" keywords in Scientific Information Database (SID), MagIran, Google Scholar, Science Direct, PubMed and Scopus databases. Data were analyzed using meta-analysis and random effect model methods. Heterogeneity between the studies was evaluated using I2 test. Data were analyzed using Stata software version 11.2.


Results
The total prevalence of metabolic syndrome was 44% (95% CI: 35% to 53%). The highest prevalence of sleep apnea distinguished by the disease belonged to patients with sleep disorders (74%, 95% CI: 66%-82%), diabetes mellitus (61%; 95% CI: 46%-76%) and cardiovascular disease (55%; 95% CI: 47%-63%).


Conclusion
Given high prevalence of sleep apnea in Iran, identifying people at risk and providing instructional materials for controlling and treating sleep apnea is necessary.


INTRODUCTION
Obstructive Sleep Apnea (OSA) is a sleep disorder that is characterized by recurrent episodes of partial or complete obstruction in the upper airways or recurrent arousals during sleep (1). Sleep apnea can lead to several problems, such as morning headaches, fatigue, impairment in daily functioning, memory loss, depression, and impotence in men, and is also related to more serious problems, such as cerebrovascular disease, cardiovascular disease, and motor vehicle accidents (2). Various studies have shown that untreated sleep apnea due to intermittent hypoxia, increased sympathetic nervous system activity, and changes in the chest cavity pressure is related to stroke, cardiac arrhythmia, cardiovascular disease, diabetes mellitus, increased blood pressure, and reduced quality of life (3)(4)(5)(6)(7)(8). Because during airway obstruction most patients with sleep apnea are asleep and not aware of their apnea, this condition is often remains undiagnosed (9,10).
Chance of death or cardiovascular disease in patients with sleep apnea is estimated to be 2.5 and 4.5, respectively (11). Old age, smoking cigarette, alcohol consumption, male gender, menopause, race, facial abnormalities, and nasal obstruction are among the other risk factors for sleep apnea (3,12). Sleep apnea can occur at any age; one in every 5 adults has mild sleep apnea and one in every 15 adults has moderate sleep apnea (13). Different

Article selection and data extraction
First, we collected all articles in which the keywords had been mentioned. Based on suggestion for reducing publication bias (16), all observation studies with a sample size of above 60 were included in the study. Only the studies were selected that met the inclusion and exclusion criteria. The exclusion criteria were as follows: unrelated to the topic, using treatment interventions for patients with sleep apnea, and lack of access to article full text. Two researchers independently examined article titles and abstracts based on the inclusion and exclusion criteria, separated the related contents, and extracted the full texts of the articles. If the two researchers disagreed on the selection of an article, the final decision was made by the correspondent author who is expert in meta-analysis. The methodological quality of the studies was examined using an instrument commonly used in the Iranian and non-Iranian studies. This instrument assessed 5 aspects of the articles, including study design, comparison group, describing the characteristics of participants, sample size, and detailed description of the instruments used to collect data. A score from 0 to 3 was assigned to each aspect.
Articles with a score from 0 to 5 were regarded as having poor methodological quality, 6 to 10 as having average methodological quality, and above 10 as having strong methodological quality (17,18). In order to analyze the articles, a form was used that asked about the following information: Name of the first author, articles' country of publication, articles' year of publication, sample size, and number of people with sleep apnea in the population studied. Article selection and screening was based on the PRISMA statement (19). Finally a total of 42 articles were selected for the analysis.

Statistical analysis
Because prevalence rate has a binomial distribution, the variance for each study was calculated through calculating the variance for binomial distribution. Weighted means were used to aggregate the prevalence rates reported by different studies, and the weight assigned to each study was its inverse variance. The I 2 index was used to examine the heterogeneity of the data. Heterogeneity was classified into three categories: less than 25% (low heterogeneity), 25 to 75% (moderate heterogeneity) and more than 75% (high heterogeneity). Due to heterogeneity of the data, a random effects model was used to aggregate the studies and for the joint estimation of the prevalence rate. The meta-regression    Table 1.